Data Storage Devices (DSDs) are often used to record data onto or to reproduce data from a storage media. One type of storage media includes a rotating magnetic disk where a magnetic head of the DSD can read and write data in tracks on a surface of the disk, such as in a Hard Disk Drive (HDD).
In the case of an HDD or other DSDs using a disk storage media, certain areas of the disk may provide for faster access when reading or writing data on the disk. For example, an Outer Diameter (OD) portion of the disk can allow for data to be read or written more quickly than at an Inner Diameter (ID) portion of the disk due to the greater circumference of the disk at the OD portion. The greater circumference at the OD portion allows for more of a track at the OD portion to be read or written for a given amount of rotation of the disk than in the shorter tracks at an ID portion of the disk.
Some DSDs with disk media can take advantage of the faster write speed by using a Media Based Cache (MBC) to quickly cache data in the MBC that is later written to its originally intended location on the disk when the DSD is not busy servicing other commands. The speed performance can be attributed to several factors. First, since data is written sequentially into an MBC regardless of their addresses, writes to the MBC can be executed with little or no seek operations, relative to writing data to their ultimate locations. Second, in some implementations, an MBC located in an OD portion may take advantage of the speed improvement discussed above.
Although this use of an MBC can generally improve the performance of a DSD in servicing commands, the performance of the DSD may change significantly when the MBC becomes full. In one aspect, the performance of the DSD is affected because new write commands can no longer be quickly written in the MBC after it is full. In another aspect, the DSD may need to take more time away from performing other commands in order to relocate data from the MBC to its originally intended location on the disk to make room in the MBC. Both of these aspects can result in a significant change in performance as seen from a host issuing read and write commands to the DSD.